Inline Power (also known as Power over Ethernet and PoE) is a technology for providing electrical power over a wired data telecommunications network (such as, for example, the well-known Ethernet) from power source equipment (PSE) to a powered device (PD) over a link section. The power may be injected by an endpoint PSE at one end of the link section or by a midspan PSE along a midspan of a link section that is distinctly separate from and between the media dependent interfaces (MDIs) to which the ends of the link section are electrically and physically coupled.
PoE is a specific form of Inline Power and is defined in the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) Standard Std 802.3af-2003 published 18 Jun. 2003 and entitled “IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements: Part 3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications: Amendment: Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI)” (herein referred to as the “IEEE 802.3af standard”). The IEEE 802.3af standard is a globally applicable standard for combining the transmission and reception (collectively: “transceiving”) of Ethernet packets with the transmission and reception of DC-based power over the same set of wires in a single Ethernet cable. It is contemplated that Inline Power will power such PDs as Internet Protocol (IP) telephones, surveillance cameras, switching and hub equipment for the telecommunications network, biomedical sensor equipment used for identification purposes, other biomedical equipment, radio frequency identification (RFID) card and tag readers, security card readers, various types of sensors and data acquisition equipment, fire and life-safety equipment in buildings, and the like. The power is direct current, floating 48 Volt power currently available at a range of power levels from about 4 watts to about 15 watts in accordance with the standard. There are mechanisms within the IEEE 802.3af standard to allocate a requested amount of power. Other proprietary schemes also exist to provide a finer and more sophisticated allocation of power than that provided by the IEEE 802.3af standard while still providing basic compliance with the standard. As the standard evolves, additional power may also become available. Conventional 8-conductor type RG-45 connectors (male or female, as appropriate) are typically used on both ends of all Ethernet connections. They are wired as defined in the IEEE 802.3af standard.
FIGS. 1A, 1B and 1C are electrical schematic diagrams of three different variants of PoE as contemplated by the IEEE 802.3af standard. In FIG. 1A a data telecommunications network 10a comprises a switch or hub 12a with integral power sourcing equipment (PSE) 14a. Power from the PSE 14a is injected on the two data carrying Ethernet twisted pairs 16aa and 16ab via center-tapped transformers 18aa and 18ab. Non-data carrying Ethernet twisted pairs 16ac and 16ad are unused in this variant. The power from data carrying Ethernet twisted pairs 16aa and 16ab is conducted from center-tapped transformers 20aa and 20ab to powered device (PD) 22a for use thereby as shown. In FIG. 1B a data telecommunications network 10b comprises a switch or hub 12b with integral power sourcing equipment (PSE) 14b. Power from the PSE 14b is injected on the two non-data carrying Ethernet twisted pairs 16bc and 16bd. Data carrying Ethernet twisted pairs 16ba and 16bb are unused in this variant for power transfer. The power from non-data carrying Ethernet twisted pairs 16bc and 16bd is conducted to powered device (PD) 22b for use thereby as shown. In FIG. 1C a data telecommunications network 10c comprises a switch or hub 12c without integral power sourcing equipment (PSE). Midspan power insertion equipment 24 simply passes the data signals on the two data carrying Ethernet twisted pairs 16ca-1 and 16cb-1 to corresponding data carrying Ethernet twisted pairs 16ca-2 and 16cb-2. Power from the PSE 14c located in the Midspan power insertion equipment 24 is injected on the two non-data carrying Ethernet twisted pairs 16cc-2 and 16cd-2 as shown. The power from non-data carrying Ethernet twisted pairs 16cc-2 and 16cd-2 is conducted to powered device (PD) 22c for use thereby as shown. Note that powered end stations 26a, 26b and 26c are all the same so that they can achieve compatibility with each of the previously described variants.
Turning now to FIGS. 1D and 1E, electrical schematic diagrams illustrate variants of the IEEE 802.3af standard in which 1000 Base T communication is enabled over a four pair Ethernet cable. Inline Power may be supplied over two pair or four pair. In FIG. 1D the PD accepts power from a pair of diode bridge circuits such as full wave diode bridge rectifier type circuits well known to those of ordinary skill in the art. Power may come from either one or both of the diode bridge circuits, depending upon whether Inline Power is delivered over Pair 1-2, Pair 3-4 or Pair 1-2+Pair 3-4. In the circuit shown in FIG. 1E a PD associated with Pair 1-2 is powered by Inline Power over Pair 1-2 and a PD associated with Pair 3-4 is similarly powered. The approach used will depend upon the PD to be powered. In accordance with both of these versions, bidirectional full duplex communication may be carried out over each data pair, if desired.
Inline Power is also available through techniques that are non-IEEE 802.3 standard compliant as is well known to those of ordinary skill in the art.
In many cases where PDs are used, it may be desirable to provide some redundancy in terms of data and/or power delivery for cases in which equipment (hubs, switches, cable and the like) providing the power and/or data fails to continue to do so.